Is L-Glutamine an Overlooked Amino Acid Supplement?

Glutamine is the most abundant amino acid in the body (we'll dive deeper into amino acids below). Like most proteinogenic amino acids, glutamine exists as two isomers: L-glutamine and D-glutamine, the former of which is the vital isomer you find in foods and glutamine powder/supplements. (Generally speaking, the term "glutamine" is in reference to the "L" form.)

So, what does glutamine do, exactly? Well, where do we begin?

Glutamine has multifarious roles throughout the human body. Notably, it facilitates muscle protein synthesis, carbohydrate metabolism/insulin sensitivity, immune function, and gut health [1].

So, if it's the most plentiful amino acid found in the body and contained in certain foods like fish, chicken, spinach, dairy, tofu, and quinoa, how does L-glutamine supplementation fit into an active individual's diet?

Glutamine: Essential or Non-Essential Amino Acid?

Amino acids are the building blocks of protein and play a role in every body system. There are 20 amino acids used in muscle protein synthesis, and nine of these are considered essential amino acids (EAAs). They are "essential" in that we must consume them in the diet since our bodies cannot synthesize them from other nutrients.

The other 11 amino acids are produced by the body and are considered nonessential amino acids (NEAAs). However, some of these nonessential amino acids—including glutamine—are considered conditionally essential. This means they are nutritionally essential when your body is stressed, such as during times of illness or exhaustion from extensive exercise.

Hence, L-glutamine supplementation (combined with essential amino acids) is prudent for highly active gym-goers, athletes, and those who are recovering from illness or surgery.

What Are the Benefits of a Glutamine Supplement?

In recent years, there has been mixed research about the true benefits of supplemental glutamine for muscle building and weight loss. For example, L-glutamine supplementation has been found to support enhanced muscle recovery after intense exercise in some studies, while a commensurate body of evidence shows no significant difference compared to placebo [2].

But that's not to say there is no benefit to taking a glutamine supplement.

Arguably the best application for glutamine supplements is in preserving cardiovascular, metabolic, and immune functions in those who are (critically) ill or highly active [3]. Taking glutamine may also prove useful for preserving muscle mass during a cutting phase by stimulating protein synthesis and reducing muscle protein breakdown [4].

Oral L-glutamine supplementation has also been found to be beneficial for wound healing after surgery [5]. Additionally, for those with irritable bowel syndrome (IBS) or inflammatory bowel disease (IBD), there is some research that suggests L-glutamine may reduce the severity of IBS/IBD symptoms, though more research is needed on this topic [6].

Is Glutamine Supplementation Worth It?

L-glutamine supplements have always been popular in the fitness space for those looking to build strength, boost their recovery, and support their overall health. Despite the mixed results of research on supplemental glutamine for muscle building and weight loss, it's not a "pointless" supplement by any means.

Remember, L-glutamine is a conditionally essential amino acid, and it may even be necessary to supplement with glutamine depending on the circumstances. Note that you should always consult with your doctor or a trusted healthcare practitioner before adding any new dietary supplements to your routine.

Is It Possible to Have an L-Glutamine Deficiency?

Glutamine deficiency is most common during severe illness. Depending on your dietary preferences (such as vegan or vegetarian lifestyles) you may not get enough glutamine through food alone.

Granted, a glutamine deficiency is quite rare in healthy individuals, even when total protein intake is relatively low.

Are There Side Effects of L-Glutamine Supplementation?

L-glutamine rarely causes adverse events when taken appropriately (e.g. up to 20 grams daily). However, it's important to note that there has been little research into the long-term effects of high-dose glutamine supplementation; some evidence suggests that excess glutamine intake (40+ grams per day) can perturb glutamine metabolism and hinder the absorption of other amino acids [7].

In general, most people should start with a modest 5-gram dose of L-glutamine, taken either with a meal, post-workout, or during training. A second 5-gram dose may be added at a separate time.

L-Glutamine: An Amino Acid Supplement Worth Considering

L-Glutamine is the most abundant amino acid in the human body and plays ubiquitous roles throughout. For active gym-goers, an L-glutamine supplement can bolster muscle protein/glycogen synthesis, contributing to athletic performance and muscle recovery.

Taking glutamine may also support your immune health, improve gut health, and enhance digestive tract integrity. These are pertinent benefits for just about everyone.